Method of and means for forming or dressing grinding wheels used for form grinding



J HARLEY ET AL 2,286,409 5 FOR FOR OR DRESSING GRINDING USED GRINDINGFiled 959 5 Sheets-Sheet 1 June, 16, 1942. s,

METHOD OF AND MEAN WHEELS MING -FORM FOR Oct.

s. .1. HARLEY ET AL 2,286,409 METHOD OF AND MEANS FOR FORMING ORDRESSING GRINDING June 16, 1942;

WHEELS USED FOR FORM GRINDING 3 Sheets-Sheet 2 Filed Oct. 2, 1959 FIGQS.

FIG.4.

J1me 1942- 5. J. HARLEY ET AL 2,286,409 METHOD OF AND MEANS FOR FORMING0R DRESSING GRINDING WHEELS USED RM GRINDING Filed 1959 s Sheets-Sheet 5FOR F0 Oct. 2,

Patented June 16, 1942 i METHODiOF AND MEANS rQ-R FORMING QBDRESSINGGRINDING vv Ls USED For.

FORM GRINDING Stanley 'Jaffa Barley and John Ernest Wainwright,Coventry, England Application .October 2, 1939, Serial No. 297,612

Great Britain October 1, 1938 (Granted under the provisions of sec. 14,act of March 2, 1927; 357 O.

7 Claims.

This invention relates to an improved method of and means for dressingor forming the-operative surface of grinding wheels employed in formgrinding and'more particularly to the formation of grinding wheels ofthe kind having a plurality of annular serrations or cutting edges foruse in producing or finishing screw threads by a grinding operation.

It is known that if the profile of a grinding wheel of the kind referredto is formed in the axial plane section as an exact replica of the screwthread it is desired to produce or finish, the resulting thread will incertain cases be found to be inaccurate. The discrepancy is due ,to'thefact that Whereas the thread to be formed is a continuous helix, theoperative surface of the grinding wheel consists of "a plurality ofserrations which are annular. The error increases with the helix angleand is more pronounced in the case of internal grinding owing to theincreased overlap of grinding surface contact (commonly known asinterference). on opposite sides of a plane containingthe axes of thegrinding wheel and the work.

It, therefore, follows that as true form .is normally dressed in thisplane, any form produced in the work other than in said plan must .be toa more or less extent untrue.

This increased overlap results from the fact that the contactingsurfaces of ,the wheel and work in internal grinding are'bothcurved inthe same direction, whereas in the case of external grinding andcontacting surfaces are curved in opposite directions.

The object of the present invention is to provide grinding wheels-of thekind referred, to with annular-serrations or cutting edgesof such formas will produce a screw thread approximating more closely to thetheoretically correct form than has so farbeen'possible.

In forming or dressing grinding wheels of the kind-hereinreferred-to-for use in internal or'eX-' ternal form-grinding operationsby means of a tool having aform-generating motion, the improved methodconsistsinsuccessively dressing the rotating grinding wheel with thetool at different angular positions about a fixedaxis,

Where the radial or depth component of the form-grinding motionof thedressing tool is produced by means'of a rotating cam the dressing tool,according to the present invention, will be mounted so astobe angularlyadjustable about the rotational axis-of'the said cam.

In any case it is essential that the minimum distance between the pointof thedressing tool and the axis of the angular movement of the lattershall be equal to the core radius of the work in the case of internalgrinding and to the major radiusof the'work in the case of externalgrinding. v

The present-invention may be conveniently applied to thetype of wheeldressing apparatus described in British Patent No. 398,841 in which thedressing tool is'carried by two relatively movable slides one of whichhas a traversing movement in a direction substantially parallel with theaxis of the grinding wheel and is operated bya lead screw, whilst'theother slide has a reciprocatory movement towards and away from the axisof'the said wheel under the influence of a rotating cam the profile ofwhich determines the depth component of the resultant motion of the twoslides.

{The form of the serrations or cutting edges in the axial plane sectionof the grinding wheel which is produced according to the presentinvention will in no case be thetrue' thread form itis required toproduce-in thework but will be such as to produce the true form and willvary according to the diameter of the work and to the pitch and helixangle of the thread in any given case.

In the accompanying drawings:

Figure 1 is a view in end elevation of a movable'headstock carrying thework-holder and the improved wheel dressing attachment for internalgrinding.

Figure2 is a plan view thereof.

Figures 3 and 4 are detail face and edge views respectively of the wheeldressing attachment.

Figure 5 is a sectional view of the same.

Figure 6 is a diagram illustrating the operation of the dressing tool.

Figure 7 is an enlarged detail cross-sectional view of one of theserrations on the grinding wheel.

Figures 8 and 9'are views similar to Figures 1 and 2 showing theapplication of-the present invention for external grinding. 7

Like parts are designated by similar reference characters throughout thedrawings.

Referring to the constructions shown in the drawings the work holder 2and the dressing at tachment 3 are mounted alongside each other in aheadstock 4 fixed to a slide 5.

The grinding wheel 6 is rotatably mounted in a head, not shown, which iscapable of movement across the bed 1 of the machine so that the Wheelcan be moved from its position with respect to the wheel dressingattachment -3, as

shown in full lines in Figures 1, 2, 8 and. 9, to the operative orgrinding position with respect to the work-piece 8, as shown in dottedlines in the same figures.

The slide carrying the work-holder and the dressing attachment has atraversing movement along the bed of the machine, as by means of a leadscrew 9, in a direction parallel with the rotational axis of thegrinding wheel in either of the two positions of the latter.

The diamond holder ID of the wheel dressing attachment is adjustablymounted in a carrier H which itself is adjustably mounted upon a slidel2 arranged for movement toward and away from the grinding wheel in adirection at right angles to the direction of movement of theheadstock, 1. e. in a direction substantially radial to the rotationalaxis of the grinding wheel.

The movement of the slide E2 in one direction is produced by means of acam i3 fixed to a shaft 13 rotatably mounted in the headstock. The cambears against a stylus it fixed to the slide, and in the returndirection in any suitable manner, as by means of a spring or weightneither of which is shown. The said slide 12 is carried by a plate l5capable of a rocking movement about the axis of the said cam and isguided in its movement in the said plate by adjustable ball bearings asshown in Figure 3.

The movements of the slides 5 and i2 by the leadscrew 9 and cam l3respectively take place simultaneously and are of such relative andrespective extent as to cause the dressing tool to generate the formrequired in the grinding wheel in the manner hereinafter described.

The distance between the point it of the diamond and the rotationalcentre of the cam l3 when the latter is at its peak position withrespect to the stylus i4, is important and will depend upon the coreradius of the work-piece in the case of internal grinding operations andon the major radius of the work-piece in the case of external grindingoperations. The construction and operation of the wheel dressingattachment is otherwise substantially the same for dressing wheels forinternal grinding purposes as for those employed for external grind-111g.

For dressing grinding wheels for producing or finishing internal screwthreads the relative arrangement of the cam and the diamond are as shownin Figures 1 and 3, that is to say, the diamond holder is adjusted inits carrier until the distance between the point it of the diamond andthe rotational axis of the cam 53 when the latter is at its peak withrespect to the stylus M is equal to the core radius or the work to beground.

For the dressing operation the grinding wheel head is moved to bring thegrinding wheel E5 into the dressing position shown in full lines at theright-hand of Figure 1, this position being determined by means of astop which is adjustable for wheels of different diameters.

The grinding wheel 6 is first dressed in the normal way with the diamondin substantially the position shown in full lines in Figure 1, that isto say, with the point lying in a plane containing the axes of the camand grinding wheel. In this position the simultaneous movements of theslides 5 and E2 in directions at right angles to each other under theinfluence of the lead screw s and cam l3 respectively, will cause thediamond to form, the rotating wheel 6 with a series of annularserrations or cutting edges having a profile of substantially truethread form. The cam determines the depth component of the form and thelead screw the pitch component. After this primary dressing of thewheel, the plate 15 carrying the slide l2 and diamond carrier II isgiven an angular adjustment in one direction about the axis of the cam,by means of the handle 127, as represented in one of the dotted linepositions in Figure 1, and more clearly in Figure 6. When the wheel isagain dressed with the diamond in the new angular position in relationto the cam l3, an interference takes place between the diamond and oneflank of the serrations on the wheel and a certain amount of material isremoved therefrom. At the end of this second dressing the plate carryingthe slide and diamond carrier is given an angular movement in thereverse direction to an equal extent in relation to the cam. The wheelis now again dressed when the interference between the diamond and wheelresults in a similar removal of material from the other flank of theserrations. This process is repeated at increasing angular positions ofthe tool carrier equally in both directions until the angular positionis such that the point of the diamond is clear of the serrations. Theresult produced is represented in Figure 7 in which the cross-sectionalshape of the serrations produced by the primary dressing is shown indotted lines and the final shape as produced by the subsequent dressingoperations in full lines. The efiect of the subsequent dressings, aswill be seen, is to remove material from the flanks of the serrations ina progressive manner from the root to the crest.

If a grinding wheel having annular serrations formed or dressed in themanner above described is now transferred to its grinding position withrespect to the work, as shown in dotted lines at the left-hand of Figurel, and whilst rotated is traversed through the latter with the properfeed it will produce an internal screw thread which is a closerapproximation to the ideal true thread form than would be obtained fromthe same wheel if the above described dressing operation had ceased atthe end of the primary dressing.

If in dressing the wheel in the manner above described the wheel ismounted to rotate about an axis at right angles to the helix of therequired screw thread the result will be to form a grinding wheel inWhich the positions of the effective portions of the several serrationsvary, progressively from a position near the root at each end of thewheel to a position near the crest at the middle of the wheel. The wheelwill also be of a more or less concave shape in cross-section at theroot and crests of the serrations.

In the application of the present invention in the formation of grindingwheels of the kind herein referred to for use in external grindingoperations, the position of the point 16 of the dressing tool withrespect to the cam l3 will be substantially as shown in Figure 8 and 9,that is to say, the position of the diamond point with respect to therotational axis of the cam when the latter is at its peak position withrespect to the stylus on the slide must be adjusted until the distancebetween the diamond point and the axis of the cam is equal to the majorradius of the work-piece. When this adjustment has been made the wheelis dressed in substantially the same manner as above described withreference to wheels for internal grinding operations with similarresults on the cross-sectional form of the serrations and on theirefiective diameters.

We claim:

1. Apparatus for forming and dressing grinding wheels used forform-grinding operations, comprising a slide, means for moving the samein a direction substantially parallel with the rotational axis of thegrinding wheel, a second slide capable of angular adjustment upon thefirst slide about a fixed axis, a dressing tool adjustably mounted onsaid second slide, a cam rotatable about said fixed axis and adapted tocause the second slide to move towards and away from the axis of thegrinding wheel irrespective of the angular position of said secondslide, the movement of the first slide and the movement of the secondslide under the influence of the cam being simultaneous and of suchrelative and respective extent as in combination with angular adjustmentof said second slide about the axis of the cam will produce the requiredform in the grinding wheel.

2. Apparatus for forming and dressing grinding wheels used forform-grinding operations,

comprising a slide, means for moving the same t in a directionsubstantially parallel with the rotational axis of the grinding wheel, asecond slide capable of angular adjustment upon the first slide about afixed axis, a dressing tool adjustably mounted on said second slide, acam rotatable about said fixed axis and adapted to cause the secondslide to move towards and away from the axis of the grinding wheelirrespective of the angular position of said second slide, the distancebetween the point of the dressing tool and the rotational axis of thecam when the latter is at its peak position with re spect to the secondslide being equal to the core radius of the work-piece in the case ofinternal thread grinding operations and to the major l radius of thework-piece in the case of internal of said cam, said slide also havingan angular adjustment about the rotational axis of the latter, themovements of said headstock and. slide under the influence of thelead-screw and cam respectively for wheel dressing purposes beingsimultaneous and of such relative and respective extent as to cause thedressing tool when moved from one position to another about the axis ofthe cam to generate the required form in the grinding wheel.

4. Dressing means for grinding wheels wherein the wheel is mounted forrotation on a machine bed, comprising a main slide mounted on said bedadjacent said grinding wheel for linear movement towards and away fromsaid wheel in a direction parallel to the rotational axis thereof, andmeans for producing such linear movement, in combination with a toolcarrying slide mounted on said main slide for reciprocation at rightangles to the linear movement thereof and to the rotational axis of saidwheel, said tool carrying slide being disposed for angular adjustmentabout an axis parallel to the rotational axis of said grinding wheel,and means for causing reciprocation of said tool carrying slideirrespective of its angular position about said axis comprising a camrotatable about the axis of angular adjustment of said tool carryingslide and in operative engagement therewith to cause reciprocationthereof.

5. A device of the character described comprising a main slide mountedfor linear movement, and a tool carrying slide mounted on said mainslide for reciprocation in a transverse direction, said tool carryingslide being also disposed for angular adjustment about a linear axis, incombination with a cam mounted on said main slide for rotation about theaxis of angular adjustment of said tool carrying slide and in operativeengagement therewith to cause reciprocation of said slide during linearmovement of said main slide irrespective of the angular position of saidtool carrying slide.

6. The method of using a dressing tool to dress a grinding wheel havinga series of annular serrations on its radial peripheral operating face,comprising rotating said wheel, and during such rotation traversing saidtool across the operative face of said wheel while maintaining the toolin a fixed position of angular adjustment about an axis parallel to theaxis of said wheel, and simultaneously reciprocating said tool at rightangles to the axis of said wheel in such a manner as to form theserrations thereof into true thread form, and thereafter, duringcontinued rotation of said wheel, while fixedly maintaining said tool ina different position of angular adjustment about said axis parallel tothe axis of said wheel, again traversing said tool across said wheelwhile simultaneously reciprocating said tool in such manner that thereciprocating movements are of the same extent and fall in the sameaxial positions relative to said wheel respectively as during said firsttraverse.

'7. Dressing means for grinding wheels for grinding screw-threads incylindrical faces of work-pieces, said dressing means being of the typewherein the wheel is mounted on a machine bed for rotation about arelatively fixed axis and comprising a main slide mounted on said bedfor linear movement in a direction parallel to said relatively fixedaxis and means for causing such movement, in combination with a dressingtool, an auxiliary slide carrying said dressing tool and mounted on saidmain slide for oscillation about an axis parallel to said relativelyfixed axis and disposed for reciprocation in a radial direction relativeto the path of oscillation thereof, the distance between the point ofsaid dressing tool and the axis of oscillation when said tool point isat the extreme end of its reciprocatory movement away from the axis ofoscillation being substantially the same as the length of the radius ofthe circle defined by the crests of the threads of the work-piece, andautomatic means for causing such reciprocation of said auxiliary slideand said dressing tool during movement of the main slide and incoordination therewith.

STANLEY JAFFA HARLEY. JOHN ERNEST WAINWRIGHT.

